1. Field of the Invention
This invention relates to electrical cabling and, more particularly, to an electrical slickline cable having two conductive stress members for carrying the tensile loads applied to the cable.
2. Description of Related Art
In the oil and gas industry, well intervention and logging equipment must often be deployed into, and retrieved from, a well by means of a cable supported at the earth's surface. Slickline tools are typically deployed downhole using a wire payed out from a drum and guided over two or more sheaves before entering the well; Steel wires are generally chosen for such service to meet the rigorous physical requirements of the service while maintaining tensile strength without sustaining damage. Such steel wires are not typically used to communicate electrical signals to the attached tool or tools. The wellhead is sealed around the wire by means of a stuffing box using elastomeric seals, which necessitates a smooth outer surface on the wire, as opposed to grease-injected sealing hardware, which is compatible with served or braided cable surfaces.
In many oilfield applications it is necessary to use a cable having a smooth outer surface that is also capable of effectively conducting electrical signals. Such cables typically employ copper wire cores that, although effective electrical conductors, lack sufficient physical strength to carry the tensile load to which the cable is subjected. The load-bearing capability of such cables is typically provided by an outer metal tube surrounding the electrically conductive core and any insulating layers. Schlumberger Technology Corporation of Sugar Land, Tex., U.S.A. uses a conductive slickline cable, designated CSL-A (H400254), that comprises a solid copper wire core, a TEFLON (polytetrafluoroethylene and perfluoroalkox polymers and a trademark of E. I. du Pont de Nemours and Company of Wilmington, Del., U.S.A.) insulating jacket, and a serve of copper wires on the outer diameter of the insulating jacket. A 316L stainless steel tube is formed, welded, and drawn over the core and insulating jacket to form a snug fit. The drawing process work hardens the tube so as to achieve maximum physical properties, specifically tensile strength in the axial direction. However, while this cable has good telemetry capability, its tensile strength and fatigue life are limited to those of the stainless steel tube alone, with the copper core adding little or no tensile strength.
Similar conductive slickline cables utilizing a copper core and a single outer tube of various stainless steels are supplied by Shell Line LLC of Calgary, Alberta, Canada and Danum Well Services of Doncaster, England.
The present invention is directed to overcoming, or at least reducing, the effects of the problems set forth above by providing a conductive slickline cable having an insulated conductor, with the physical robustness of a slickline wire, enhanced tensile strength, and a smooth, round outer surface for sealing purposes. The invention utilizes the space inside the outer tube to increase the overall load carrying capacity of the cable.